If I place the copyright later in the file, say, after the synopsis, or even at the end of the file, would someone misusing my code be able to get away with saying: "Oh, well you're supposed to put the copyright at the beginning, its not fair to expect me to go looking around for it".
Either the person "misusing" your code is doing something they are allowed to do under copyright law or they are doing something they need the copyright holder's permission to do under copyright law.
A copyright notice can't take away any rights anyone already has. A book can't have a copyright notice that says, "By the way, you may not read this book on Sundays". A mere notice can't take away anyone's rights.
So if they're doing something they don't need special permission to do under copyright law, then that's the end of it. It doesn't matter what the copyright notice says if you're doing something copyright law allows you to do anyway.
But what if they're doing something they're not allowed to do under copyright law without permission of the copyright holder? Then how would them saying they didn't see the copyright notice change anything? They would just be admitting that they had no reason to think they had a license or other permission to do something that the law requires them to get permission to do.
The structure of copyright law is as follows: Normally, if you own something, you can pretty much do whatever you want with it. Without copyright law, if I owned a book, I could read it, copy it, perform it in public, or otherwise do pretty much anything except throw it at someone else's head.
Copyright law changes this. Copyright law sets aside specific things that are not rights of possession. It separates the physical possession of a book from the right to make copies of the creative contents of that book. The things that copyright law separates from rights of possession then become things you need the copyright holder's permission to do, regardless of your physical possession of copies of a work.
Anything not separated from rights of possession by copyright law are rights that anyone who legally possesses the work may exercise. For examples, US law does not separate use. So anyone who lawfully possesses a copyrighted work may use it in the ordinary way. So you don't need permission to read a book you own or watch a DVD you own.
Rights separated by copyright law include making copies, distributing to the public, performing in public, making creative follow on works, and so on. These are things you always need the copyright holder's permission to do and if you can't get it for any reason, you simply can't do those things.
Copyright notices really only do two things:
They inform people who the copyright holder is. This can be helpful if you're trying to contact the copyright holder to get additional rights.
They can offer additional rights that you wouldn't otherwise have. For example, a copyright notice can include permission to make copies or permission to perform the work in public.
But that's about it. Copyright notices are not required and they cannot take any rights away. Nobody is under any obligation to read them or consider them if they don't want to. They are not binding on anyone but the person who wrote the notice.